In a device that handles an optical disk such as a CD or DVD, an optical pickup irradiates the information recording surface of the optical disk with a beam of light, receives reflected light from the optical disk while carrying out focus control, and reads out recorded data. In addition, to perform the focus control, a focus search is carried out before starting the readout operation. In the focus search, a focus error signal indicating a light receiving state of the optical pickup is generated; a predetermined level of the signal is set as a focus pull-in level in advance; the object lens of the optical pickup is moved in the direction perpendicular to the recording surface of the optical disk; and when the focus error signal reaches the focus pull-in level by the movement, the focus pulling-in is carried out which adjusts the focus of the object lens by controlling the movement. In this way, the focus pulling-in is carried out using the predetermined fixed value of the focus pull-in level.
In addition, there is a device that has a focus error signal learning means; learns the maximum value and minimum value of the focus error signal level during a learning period; and carries out focus pulling-in, that is, adjusts the focus of the object lens by using the maximum value and minimum value the focus error signal learning means learns during the pull-in control period (see Patent Document 1, for example). Incidentally, in the learning described above, level variations of the focus error signal due to temperature changes are not considered.
Patent Document 1: Japanese Patent Laid-Open No. 2000-155953 (Pages 4-6 and FIGS. 1 and 2)
With the foregoing construction, since the conventional optical disk drive utilizes the fixed or initial focus pull-in level on startup when carrying out refocusing pulling-in such as when the focus control gets out of place because of disturbance like scratches or vibrations of an optical disk during playback operation or data readout, or when carrying out a focus jump such as when repeating STOP/PLAY operation or handling a multilayer structure optical disk, it becomes difficult to carry out the focus pulling-in reliably because of the temperature within the optical disk drive. In particular, if the level of the focus error signal varies due to self-heat-generation of the optical disk drive or changes in the ambient temperature, a problem arises in that it becomes difficult to carry out the refocusing pulling-in or a focus jump well.
The present invention is implemented to solve the foregoing problem. Therefore it is an object of the present invention to provide an optical disk drive capable of carrying out the focus pulling-in in accordance with the temperature within the device.